When we house train we watch our pup all the time they are out of their bed. If they look like they're about to crouch down you can scoop them up and quickly take them outside. We also take them out when they wake up, after a game, after food and every 20 minutes or so anyway. Lots and lots of praise is given when they "go" outside, and accidents are just cleaned up without any fuss whatsoever. We always take them out on the lead and as they're about to go we say a trigger word - we use "busy". Our dogs will go to the toilet on command now, which is very useful. It's a very intensive time, but, put the work in, and a pup will train very quickly. A pup will already have some idea as they are trained by their mother not to soil their bed. You just need to build on this.